1. Field of the Invention
The present invention is generally related to a lithography method, and more particularly to a positive and negative dual function magnetic resist lithography method.
2. Description of the Prior Art
Perovskite-type oxides (ABO3) become an important research focus for multifunctional materials in recent years due to its various special properties, such as paraelectric, piezoelectric, and photoelectric properties.
According the report in Materials Chemistry and Physics, 77, 639-646, (2002), perovskite-type oxides can be prepared by ball-milling La2O3, MnCO3, and SrCO3 raw materials for 24 hrs and then sintering at 1000° C. for 2 hrs and maintaining at 1250° C. for 5 hrs.
According to another report in J. Mater. Res., Vol. 15[5], 1161-1166 (2000), solid-state reactions is also used to prepare perovskite-type oxides. Lanthanum strontium manganese oxides and carbonates, such as La2O3, MnCO3, and SrCO3 with proper molar ratio, are sintered at 1200° C. for 12 hrs, ball-milled, cold isostatically pressed, and then sintered at 1450° C. for 48 hrs. Although the process is simpler, the longer duration at high temperature is required. Besides, particle diameters are in the micron range (10−6 m). It is difficult to control compositions and uniformity.
The disadvantages of using solid-state reactions to prepare perovskite-type oxides are difficulty in the mixing process and in the composition control, and the requirement of sintering at high temperature. Therefore, liquid-phase methods, such as sol-gel method, are utilized, instead.
In the liquid-phase methods, metallic salts are used as starting raw materials, such as acetates (J. Am. Ceram. Soc., 75[4], 964-970 (1992)) and nitrates (J. Am. Ceram. Soc., 75[1], 201-202 (1992)). Phase promoters are poly(acrylic acid) (J. Am. Ceram. Soc., 75[1], 201-202 (1992)), poly(vinyl alcohol) (J. Am. Ceram. Soc., 80[10], 2702-2704 (1997)), citric acid (J. Mater. Res., 9[4], 986-991 (1994)), and so forth.
Using liquid-phase methods to synthesize perovskite crystal phase oxides, the lanthanum strontium manganese oxides usually can be formed at the temperature below 500° C. For example, in the nitrate-poly(acrylic acid) system, the crystal phase with perovskite structure can be fabricated by using poly(acrylic acid) to make the precursor solution become gelation and then sintering at 400° C. for 6 hrs.
In the nitrate-acetate-citric acid system reported in J. Mater. Res., 9[4], 986-991 (1994), thermally induced anion oxidation-reduction (auto ignition) reaction is utilized to form the crystal phase of the lanthanum strontium manganese oxides. The particle diameter obtained by this method is larger than that in the nitrate-poly(acrylic acid) system.
According to the report in J. Am. Ceram. Soc., 80[10], 2709-2713 (1997), the lanthanum strontium manganese acrylates are used as the precursor solution to be spin-coated on silicon wafers and fused quartz substrates. The perovskite crystal phase is formed by multiple coatings to increase film-thickness and then calcination at 850° C.
According to the report in J. Am. Ceram. Soc., 80[10], 2702-2704 (1997), the lanthanum strontium manganese oxalates are used as starting materials and PVA (poly(vinyl alcohol)) is then added so as to form the precursor solution. The precursor solution is spin-coated on the fused quartz substrate and then sintered at 550° C. to thereby form the perovskite crystal phase. Compared to the conventional solid-state synthetic method, the liquid-phase method for preparing the perovskite crystal phase takes lower sintering temperature.
The Taiwan patent No. 574608 discloses a zwitterresist lithography for positive resist and negative resist processes by varying the exposure doses of electron beams to prepare positive and negative resists in the same resist layer. When the exposure dose is low, polymeric bonding is broken in the resist layer to be removable during the developing process and thereby to show the characteristic of positive resists. On the other hand, when the exposure dose is increased to a threshold value, the increased energy causes the separated polymeric molecules to form polymeric blocks to have crosslinking reactions and thereby to show the characteristic of negative resists. However, magnetic resist material is not provided by neither this Taiwan patent nor the commercial resist materials as well as the requirement of developing with water-soluble solvents. In light of the above problems, it is an important research topic in the development of a new magnetic resist with both positive and negative resist properties, water-soluble solvent developable property, and capability of preparing nano-scale patterns.